In a wavelength division multiplexing (WDM) network, a wavelength may be newly added in some cases. When a new wavelength is added to an existing optical path, it is determined whether a design value of transmission quality in the existing optical path reaches a required value of transmission quality required when the new wavelength is added. For example, the worst value of a parameter for determining transmission quality such as an optical fiber or an optical component is used as the design value.
When it is determined that the design value of the transmission quality in the existing optical path reaches the required value of the transmission quality, the new wavelength may be added to the existing optical path. On the other hand, when it is determined that the design value of the transmission quality in the existing optical path does not reach the required value of the transmission quality, the transmission quality is ensured by disposing a regenerator (REG) (a regenerative repeater) in the existing optical path in order to add the new wavelength.
In the WDM network, a light wavelength separating device separates a wavelength A in which a monitoring control signal is carried, and applies the separated monitoring control signal to a monitoring control signal transmission/reception circuit. A technique is known in which an AGC circuit controls an amplifier on the basis of an output of the monitoring control signal transmission/reception circuit and an output of a monitor so as to make a gain of an optical amplifier constant (see, e.g., Japanese Laid-Open Patent Publication No. 2004-173309).
Related technologies are disclosed in, for example, Japanese Laid-Open Patent Publication No. 2004-173309.